1. Field of the Invention
The invention relates to distribution of digital content.
2. Related Art
Distribution of digital content for media streams, such as for example movies, is subject to several problems. One problem is that it is easy to make exact copies of digital content, thus allowing any recipient of that content to redistribute it, whether authorized or not. It would be advantageous to be able to distribute digital content, particularly digital content for media streams, without fear of its unauthorized distribution. This would be particularly advantageous when it is desired to distribute digital content using a communication link, such as for example a computer network or other technique for distribution to end viewers (for example, either on demand, in anticipation of future demand, or in response to something else).
One known solution is to mark digital content with a “fingerprint,” that is, information sufficient to identify the recipient of the digital content, so that an unauthorized distributor of the content can be determined, thus hopefully deterring potential unauthorized distributors. Other known solutions include marking digital content with a “watermark,” that is, information sufficient to identify the digital content itself. Thus for example, if a recipient of the digital content distributes it without authorization, that recipient can be identified and called to account for that activity. However, fingerprinting and watermarking of digital content is subject to attacks by recipients, by which those recipients might be able to erase or alter the fingerprint or watermark, or to otherwise make copies of the digital content from which it is difficult or impossible to determine the unauthorized distributors. Possible attacks include (1) alteration or erasure of the fingerprinting or watermarking information, (2) collusion among multiple recipients to mix fingerprinting or watermarking information together, and (3) combinations of multiple attacks.
Known techniques for countering attacks against fingerprinting information have been directed to detecting colluders. However, such known techniques, to the extent they are effective, are also subject to another important problem—avoiding accusation of innocent recipients. Moreover, such known techniques are relatively ineffective when the number of colluders is more than a few. For example, one known technique can be defeated by as few as 8–10 colluders, even when using millions of bits of embedded fingerprinting or watermarking information.
It would be advantageous to provide a technique by which attacks against fingerprinting and watermarking can be thwarted, with the effect that recipients responsible for distributed digital content can be identified notwithstanding such attacks.